An AC type surface discharge plasma display panel, which has become dominant in plasma display panels (hereinafter simply referred to as a panel), has a front plate and a rear plate oppositely disposed with each other and a plurality of discharge cells therebetween.
The front plate is formed of a front glass substrate, a plurality of display electrodes, a dielectric layer, and a protective layer. Each of the display electrodes is formed of a pair of a scan electrode and a sustain electrode. On the front glass substrate, the display electrodes are arranged in parallel with each other, and over which, the dielectric layer and the protective layer are formed to cover the display electrodes.
The rear plate is formed of a rear glass substrate, a plurality of data electrodes, a dielectric layer, a plurality of barrier ribs, and a phosphor layer. On the rear glass substrate, the data electrodes are arranged in parallel with each other, and over which, the dielectric layer is formed to cover them. On the dielectric layer, the barrier ribs are formed so as to be parallel with the data electrodes. The phosphor layer containing phosphors for emitting red (R), green (G), and blue (B) is formed on the surface of the dielectric layer and on the side surface of the barrier ribs.
The front plate and the rear plate are sealed with each other so that the display electrodes are orthogonal to the data electrodes. The discharge space formed between the two plates is filled with discharge gas. The discharge cells are formed at which the display electrodes face the data electrodes.
In the panel with the structure above, a gas discharge occurs in each discharge cell and generates ultraviolet light, which excites the phosphors of R, G, and B to have light emission for color display. One pixel on the panel is formed of three discharge cells containing phosphors R, G, B, respectively.
In the panel operation, a sub-field method is typically employed. In the sub-field method, one field period is divided into a plurality of sub-fields (hereinafter, simply referred to as sub-fields). Gradation display on the panel is attained by combination of lit cells and unlit cells in each sub-field.
Hereinafter will be briefly described the sub-field method. Each sub-field has an initializing period, an address period, and a sustain period. In the initializing period, all of the discharge cells undergo an initializing discharge for erasing previous histories of wall charges for each discharge cell and preparing wall charge necessary for an address operation. In addition, the initializing discharge generates priming (as an initiating agent, i.e., an excitation particle) that decreases discharge delay for generating an address discharge with stability. In the address period that follows the initializing period, scan pulses are sequentially applied to the scan electrodes; at the same time, address pulses suitable for image signals are applied to the data electrodes. The application of the pulses generates a selective address discharge between the scan electrodes and the data electrodes, by which wall charge is formed selectively on the electrodes. In the sustain period, a predetermined number of sustain pulses suitable for luminance weight is applied between the scan electrodes and the sustain electrodes. The application of the pulses allows a discharge cell where wall charge has been formed by the address discharge to undergo a sustain discharge for light emission.
In the sub-field methods, Japanese Unexamined Patent Application Publication No. 2000-242224 (hereinafter, patent document 1) introduces an improved driving method. According to the method, providing any one of an all-cell initializing operation and a selective-cell initializing operation in the initializing period reduces light emission as possible from cells with no contribution to gradation display, enhancing the contrast ratio. In the all-cell initializing operation, all of the discharge cells relating to image display undergo the initializing discharge, whereas in the selective-cell initializing operation, only a discharge cell in which the sustain discharge has occurred in the previous sub-field selectively undergoes the initializing discharge.
To show black partly or entirely on the panel, the discharge cells having pixels of black are maintained in non-emission state during one field period. Hereinafter, such discharge cells are referred to as non-emission discharge cells.
In that case, the scan electrodes sequentially undergo application of the scan pulses, while the data electrodes at the non-emission discharge cells undergo no application of the address pulses in the address period. As a result, the non-emission discharge cells have no address discharge in the address period, and therefore, the cells have no sustain discharge in the sustain period. In this way, black color is partly or entirely shown on the panel.
At that time, for obtaining a higher contrast between images, the luminance of black color should preferably be minimized for the area partly or entirely filled with black. However, even in the driving method introduced in patent document 1, the luminance of black cannot be lowered to zero because of a weak discharge that occurs in all of the discharge cells in the all-cell initializing operation. Thus the luminance of black on the panel has not satisfactorily lowered.
To address the problem, the inventor tried a driving method where a field that contains the all-cell initializing operation (hereinafter, an all-cell initializing field) and a field that contains the selective-cell initializing operation only i.e., contains no all-cell initializing operation (hereinafter, a selective-cell initializing field) are set at a predetermined ratio. However, the selective-cell initializing field with no all-cell initializing operation has a problem of poor priming due to the fact that the priming caused by discharge rapidly decreases with passage of time. Because of such insufficient priming, some sub-fields have increase in interval between application of the pulses—the scan pulses for the scan electrodes and the address pulses for the data electrodes—and discharge generation (hereinafter, the increased interval is referred simply to as discharge delay). Due to the discharge delay, a discharge does not properly occur within the time of the application of the scan pulses to the scan electrodes (hereinafter, scan-pulse width). The inconveniences have invited address failure, resulting in unlit discharge cells.
patent document 1: Japanese Unexamined Patent Application Publication No. 2000-242224